The present invention involves a molding machine which utilizes toggle linkage mechanisms to develop the necessary mold lockup forces. More particularly, the present invention involves a molding machine which is improved by virtue of a molding machine which is improved by virtue of a smaller overall size and cost and a high sensitivity for triggering lockup.
Prior art molding machines as shown in U.S. Pat. No. 3,452,399 have used different sets of actuating mechanisms for large scale motions of the mold portions and mold lockup, even though a single actuating means of suitable size could be used for both purposes. The advantages of using separate actuating mechanisms can be attributed to the grossly different requirements for a mold closing system and a mold lockup system. Generally, the mold closing system must produce large scale displacements with relatively small forces while, on the other hand, the lockup system must produce relatively small displacements, but large lockup forces.
In the prior art machines such as shown in U.S. Pat. No. 3,452,399, the actuator for the lockup mechanism is situated along the central axis of the machine and actuates a pair of symmetrically disposed toggle linkages which are brought into operation after traversing actuators have produced the large scale movements that bring the mold portions into engagement. Since the lockup actuator which is a piston and cylinder assembly extends between a stationary platen and the toggle mechanisms, a large displacement of the piston in the assembly is needed to accommodate the movement produced by the mold traversing actuators and the actuator projects a substantial distance rearwardly of the machine. The projecting actuator greatly increases the overall length of the machine. In addition, the fluid capacity of the machine is increased and the various components such as pumps, coolers and filters must be increased to handle the higher capacity. All of the increases in size correspond to increased cost of the machine.
The lockup mechanism for a thermoforming machine illustrated in U.S. Pat. No. 3,632,272 employs two toggle mechanisms which are actuated by a piston and cylinder assembly. Protrusion of the actuating assembly is avoided by connecting the cylinder between a crosshead joined to the toggle mechanisms and the moving platen which is locked by the toggle mechanisms. Additionally, however, the total displacement of the moving platen is relatively limited since the thermoforming process is carried out with sheets and the resulting product does not require large clearances to be removed from the mold.
Accordingly, it is a general object of the present invention to provide a molding machine which has a reduced cost and overall length and which at the same time can be accurately triggered to produce lockup forces at the appropriate time.